LEGO Interface A

Nowadays computers are everywhere. And you can connect almost anything to a computer thanks to USB – truly a Universal Serial Bus.

But in 1986 computers were not so omnipresent. Computers were expensive and difficult to connect. Apple had the SCSI bus, IBM had ISA bus and simpler systems like the ZX Spectrum had… something. You could expect to connect maybe a modem or a printer but pretty much everything else would need a custom interface card.

So in 1986 LEGO announced the Dacta Technic Interface A (1093 or 9750) and for the first time people could use LEGO Technic motors and sensors with a computer.

Interface A was meant to be connected to the printer port of the computer. This was a clever move – at that time, the only de facto standards  were the serial port (RS232) and the parallel printer port (Centronics). By choosing the printer port several systems could use the Interface A: the IBM PC, the Apple II, the Acorn BBC Micro, the Commodore C64 and the MSX (some would still require a custom adapter).

So, historically speaking, the Interface A was the grand-grand-father of the current LEGO MINDSTORMS, WeDo and BOOST products.

I was 15 by that time. I had a Sinclair ZX Spectrum 128 and was learning Basic and decided to be an Engineer. In Portugal LEGO Technic was rare and expensive and I never heard about Interface A until a few years ago.

At university I tried to make my own Spectrum interface to use some motors but gave up and made a Centronics interface to use with my PC. I was afraid to damage my pretty expensive computer so I spent weeks designing it and used optocouplers to isolate the computer from the external electronics I wanted to use. I didn’t have LEGO motors so I used walkman motors glued to LEGO plates and used rubber bands instead of gears and even made a small 3 DOF LEGO robotic arm with the bricks I had from the only Technic set I ever had before my dark age, the 8074 – Universal Set with Flex System:

So without knowing, I was designing my own Interface A Plus 🙂

My own Interface

So after my LEGO dark age I was back to robotics and LEGO and finally found out the Interface A. Interesting but useless, I don’t have a printer port anymore on any of my computers and I was not interested in making an Arduino adapter just for that.

But recently I had been experimenting FTDI devices with linux and MINDSTORMS EV3. One of the uses of the FTDI 232 familly allows bitbanging each of the pins to create a custom GPIO interface. There even are python libraries for that purpose… so I wondered if I could use an FTDI adapter with the old  Interface A? If it worked, I could use the same adapter with my laptop, my Raspberry Pi’s and of course my EV3.

Short answer: Yes I can!


Series NavigationRessurecting the LEGO Interface A >>